The present invention relates to the operation of a mobile crane and the related apparatus, and more particularly, to self-assembly of a traveling crane utilizing a self-contained lifter.
Mobile cranes have either crawler tracks for moving about a work site, or built in wheels that allow work site movement and direct over-the-road travel. If tracks are employed, the crane is moved by a tractor trailer from one site to the next. These two versions of cranes make up a substantial portion of the crane market. A significant sought after advantage is of course the ability to move from work site to work site in a very short time. In this manner, the construction company can make very efficient use of their capital equipment. In the past, this has been a particular focus for design of not only light-to-medium duty cranes, but also in recent years to heavy duty cranes. However in the past, especially in the operation of medium to heavy duty cranes, one factor remains a particular hindrance. There has usually been a need for having an attending light duty crane to assist in erecting the mast, assembling the boom, placing the counterweight units and other component parts in position and other make-ready functions before the crane can begin the work for which it is intended.
For the traveling mode of the heavy duty crane, the base unit of the crane is constructed as large and heavy as possible, subject only to the restrictions of the over-the-road travel. In other words, it is desirable to leave as much of the structure that can be, assembled as the base unit. This reduces the assembly and make ready time at the work site, as well as the disassembly work time once the crane""s work is completed and moving to the next work site is desired. In this regard, it would be very desirable to leave the boom base section attached to the crane base unit, since this is one of the heavier component parts of the crane. Other parts of the crane, such as boom sections for the upper boom, the counterweight units, the crawler tracks and other heavy component parts, may be more conveniently removed and transported on separate tractor trailers. Once at the work site, if the crane boom base can be left in place, the main boom support pins are already secure. Thus, this proposal not only substantially reduces the time for assembly, but also substantially reduces the inspection effort to insure that the crane is work-ready.
In the past, there has been some development in making a crane to be self-assembling and self-disassembling. One of the most successful approaches is shown in Applicant""s own U.S. Pat. No. 5,240,129, issued Aug. 1, 1993. The technology set forth in this patent provides for self-erecting the live mast, and then rerigging the crane using a wire rope and a hoisting drum for adding all of the other component parts, including the boom base section. This approach while the most successful to date requires some improvement in the area of limiting the special rigging in order to successfully carry it out. The installation and operation of the special rigging is time consuming in itself. After each successful assembly or disassembly of the crane the rigging must be changed to be made ready for work or transport.
Other less efficient approaches have been taken in the past. These methods share the common drawback of also needing special rigging and using the main hoist drums in order to carry the function of assembly and disassembly. An example of such a system is illustrated in U.S. Pat. No. 5,484,069, issued Jan. 16, 1996. In particular, the rigging process includes steps of repositioning the main load line from its working position over the sheave at the top of the boom and connecting it over a separate sheaves in the boom base section. This requires not only removal and rerouting of the main load line, but rerigging it through the separate sheaves on the boom base section. Such a process is not only time consuming, but also very tedious and requires several operators working together to accomplish the task and properly inspect it when completed.
Other, earlier methods have been used, but also with little success in terms of efficiently handling the assembly/disassembly operation, such as illustrated in U.S. Pat. No. 4,579,234, issued Apr. 1, 1986.
Previously, in some very light duty cranes, there have been proposals for stowing the boom over the cab of the vehicle by using hydraulic power cylinders connected adjacent the gantry, along with additional, very complicated rear mounted linkage. Such an approach is exemplified by the structure shown in the U.S. Pat. No. 3,146,893, issued Sep. 1, 1964. Clearly however, this proposal is not instructive as to some medium to heavy duty mobile cranes since leaving the boom connected for travel is not feasible due to the weight consideration.
Thus, there is identified a need for an improved method, and related apparatus for self-assembly (and disassembly) of relatively large, medium to heavy duty cranes. A particular characteristic of this approach would be to leave the boom base section connected to the base unit of the crane during travel, not only for more efficient delivery to the original customer, but more importantly for more efficient use by the contractor moving between work sites. Also, it is contemplated that this would be accomplished with a self-contained dedicated lifter in the boom base section. As a result, the assembly or erection, and disassembly of the heavy duty crane could be efficiently carried out in a much shorter time than heretofore possible, and without the need for a separate, attendant crane being on the work site. Since the main pins are left in place, the inspection time should also be reduced.
Accordingly, it is a primary object of the present invention to provide a method and a crane particularly adapted for self-assembling, and thereby overcoming the limitations and shortcomings of the prior art, as set forth above.
It is another object of the present invention to provide a self-assembling method and related apparatus for a crane in which the operations can be carried out with a self-contained lifter permanently mounted in the base section of the boom.
Another object of the present invention is to provide the method of self-assembly and disassembly utilizing hydraulic cylinder means that are mounted in a self-contained manner within the base boom section.
Still another object of the present invention is to provide a crane assembly method and related apparatus that allows self-assembly of the load handling boom, as well as all other component parts to the crane, through dedicated hydraulic cylinders housed within the confines of the boom base section.
Additional objects, advantages, and other novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention as described herein, an improved method of self-assembling and (disassembling) a crane, including a load handling boom, and the apparatus to carry out the method in an efficient manner on a self-contained basis, is provided. The crane is particularly adapted for transport, or for direct over-the-road operation in a fast turnaround time. The crane to which the concept of the present invention applies is in the medium to heavy duty range so that some component parts must be carried on separate tractor trailer transport vehicles in order to remain within the highway weight limits imposed by the U.S. and state governments.
An important feature is to provide for the boom base section to remain on the base unit or works section of the crane. While the present invention will thus be described in the preferred embodiment illustrated with respect to a particular medium/heavy duty crane, and one mounted on crawler tracks, it will be recognized that the same approach can be utilized in any form of crane having a load handling boom. Also, while the particular operation is illustrated on a mobile crane having a live mast, within the broadest aspects of the invention other approaches for assisting in the support of the boom could be used.
The method of the present invention includes bringing the component parts, such as the upper or extension sections, to the customer in the first instance, or to the work site during contractor use, on a separate truck. The boom and/or other parts are raised from the trailer bed in sequence by use of the self-contained lifter associated with the boom base section. The crane then moves, including a 180xc2x0 rotation of the upper works if desired, to a separate location for assembly of the boom and/or for attaching other component parts. The boom sections or other parts being carried are lowered in a position adjacent the ground level. The extension sections are connected together to form an upper boom for later connection to the boom base section to form the complete boom of the working crane.
As will be realized by those of skill in the art, the method steps are reversed to disassemble the crane and make ready the crane to be moved to a new work site. During the disassembly, the upper boom is disassembled, other component parts are removed, and all are placed back on the transport trailers by use of the boom base section. Advantageously, the boom base section remains connected to the base unit of the crane at all times and is dedicated to this function in the sense that no rerigging is required to make it fully operative.
Other than the boom extension sections being removed and transported to and from the work site on special trailers, the next most important parts to be handled in this manner are the counterweight units. Typically, such a counterweight unit weighs in the range of 20,000-50,000 pounds and can be easily handled by the self-contained lifter associated with the boom base section, in accordance with the present invention. For assembly, each counterweight unit is lifted from the bed of the trailer, lowered to a position adjacent the ground at a convenient location, disconnected and then lifted from the ground by the gantry assembly and moved to its normal location up on the rear of the crane base unit.
The preferred apparatus to carry out the method of the present invention includes a pair of hydraulic cylinders to form the lifter within the boom base section. The cylinders are self-contained in the base section with a lift line connected to the distal end of the piston within each cylinder. The line, such as a wire rope, extends over a sheave adjacent the distal end of the base section. An important feature is that the cylinders and the associated lift lines remain in/with the base section, respectively.
Within the broadest aspects of the present invention, the lifter may employ in lieu of the cylinders, a pair of small winches or drums for the lift lines, but it will be recognized that for incorporation in the restricted confines of the boom base section, the use of cylinders, especially because of their narrow dimensions, is preferred.
A sling may be attached to the hook on the end of each of the lines for handling the boom extensions, and other large component parts. For the counterweight units, and for other more compact parts, a load hook or other connector is attached directly to the part. When not in use carrying out the function of assembly and disassembly, the lifter lines may be snugged along the lower edge of the boom base section after simply being coupled to an attachment eye.
Still other objects of the present invention will become readily apparent to those skilled in this art from the following description wherein there is shown and described a preferred embodiment of this invention, simply by way of illustration of one of the modes best suited to carry out the invention. As it will be realized, the invention is capable of other different embodiments, and its several details are capable of modifications in various, obvious aspects all without departing from the invention. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive.